1. Field of the Invention
The present invention relates to a flat cathode ray tube, and more particularly, to a structure for damping vibration of a shadow mask that selects colors in a flat cathode ray tube (CRT).
2. Background of the Related Art
The CRT is a device for actual display of an image in an image display system, and, recently, flat CRTs are developed and put into practical use, that eliminate distortion of the image, minimize reflection of external lights, and maximize a visual range. As shown in FIG. 1, the flat CRT is provided with an external structure inclusive of a substantially flat panel 1 having fluorescent material coated on an inside surface thereof, and a funnel 2 fused on a rear half of the panel 1 by using Frit glass. The panel 1 has safety glass 1b bonded to an external surface thereof by using resin, and there is a substantially rectangular rail 3 that supports the shadow mask fitted on the inside surface of the panel 1. The shadow mask 4 with a plurality of beam pass through holes 4a is fitted on the rail 3 under a tension, for selection of colors of the electron beams. There is an electron gun 6 sealed in a neck portion 2a of the funnel 2 for emitting the electron beams 6a of R, G, B three colors, and a deflection yoke 7 on an outer circumference of the neck portion 2a for deflection of the electron beams in horizontal and vertical directions. Though a rigidity of the shadow mask 4 can be sustained by providing a curvature to the shadow mask in the related art color CRT, as explained, the rigidity of the substantially flat shadow mask 4 in the flat CRT is relatively weakened compared to the curved shadow mask in the related art actually, which causes heavy howling, vibration of the shadow mask owing to an external acoustic wave, that deteriorates a color purity of a reproduced picture.
There are different related art methods used for preventing such a howling in the flat CRT, as one of which a structure for preventing vibration of a shadow mask by using damper wire will be explained.
Referring to FIG. 2, the related art structure for damping vibration of a shadow mask by using damper wire is basically provided with a shadow mask 4 fitted to the rail, a shadow mask supporting body, on the panel 1 under a tension, and a damper wire 8 fastened by fastening members 8a and 8b for strapping the shadow mask 4. The damper wire 8 can not be welded on the rail 3 directly owing to its thin diameter, to require the fastening members 8a and 8b for gripping both ends of the damper wire 8, then, the damper wire 8 and the fastening members 8a and 8b are welded together; the damper wire 8 is assembled with the fastening members 8a and 8b before fixed to the shadow mask 4, to require many components in the fabrication of a damping structure. For preventing a shadow of the damper wire 8 from being displayed in the picture, care should be taken in welding the damper wire 8 assembly on the rail so that the damper wire 8 is located within a narrow space between the beam pass through holes 4a in the shadow mask 4. For such an accurate position selection of the damper wire 8, a non-effective region of the shadow mask 4 is formed such that a hole 4b of a preset size is positioned on the same line with the region between the beam pass through holes in the effective areas of the shadow mask 4, for positioning the damper wire 8 with reference to the hole 4b by using a camera, which requires much working time in fabrication of the vibration damping structure.
In conclusion, though a plurality of damper wires 8, in more detail, damper wire assemblies, are required to be fitted through the foregoing process for obtaining vibration damping effect, as explained, many components and complicate process are required to carry out the work. The many components and complicate process drops productivity and pushes up the cost.
Accordingly, the present invention is directed to a structure for damping vibration of a shadow mask that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a structure for damping vibration of a shadow mask, which has an optimal vibration damping condition.
Another object of the present invention is to provide a structure for damping vibration of a shadow mask, which has a simple system according to the optimal condition.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the structure for damping vibration of a shadow mask in a flat cathode ray tube includes the shadow mask fitted to a mask supporting body, and a plurality of damper wires each fastened to the mask supporting body for strapping the shadow mask between beam pass through holes in the shadow mask under tension, wherein a first order natural frequency of the damper wire falls on a range outside of a range within xc2x110% of a third order natural frequency of the shadow mask.
The shadow mask has a thickness ranging 40 xcexcmxcx9c80 xcexcm, the damper wire has a diameter ranging 65 xcexcmxcx9c100 xcexcm, and the damper wire has a tension ranging 250 gfxcx9c1200 gf excluding the resonant tension for respective damper wire diameters.
The damper wire meets a condition of       T     less than                             (                      ρ            ⁢                          (                                                2                  ⁢                                                            (                                              L                        ⁢                                                  (                          fm                          )                                                                    )                                        3                                                  n                            )                                )                2            ⁢              (                  n          =          1                )              ,
where (fm)n denotes an (n)th order natural frequency of the shadow mask, xe2x80x98Txe2x80x99 denotes a tension on the damper wire, xe2x80x98xcfx81xe2x80x99 denotes mass of the damper wire per a unit length, and xe2x80x98Lxe2x80x99 denotes a total length of the damper wire.
The shadow mask has a thickness within a range of 50 xcexcmxcx9c80 xcexcm, the damper wire has a diameter within a range of 80 xcexcmxcx9c100 xcexcm, and the damper wire has a tension within a range of 250 gfxcx9c500 gf.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.